Problem Preparing File for Downloading

My site is set up to backup with Jet Pack and it appears the backups are working. However, when I try to download the files, I get this error:

Problem preparing your file

There was a problem preparing your backup for downloading.

I have tested this on several different backups and I get the same error each time. I have successfully downloaded backups in the past (the last time about a month ago). Can anyone help me figure out what is wrong?

Thanks!